Low dosage kinetic hydrate inhibitors for natural gas production systems

ABSTRACT

Copolymers containing acryloylmorpholine and vinylimidazole, and optionally vinylcaprolactam and/or n-vinyl pyrrolidone, have shown superior results in hydrate inhibition tests at conditions of 7° C. subcooling dosed at 1 vol % based on the water cut of the system fluids. The copolymer product has also passed high TDS (total dissolved solids) brine compatibility tests and secondary property tests including foaming and hot injection tests which make it useful as a kinetic hydrate inhibitor in gas production systems susceptible to the formation of natural gas hydrates.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application from U.S. Ser. No.13/648,491 filed Oct. 10, 2012, which issued ______ as U.S. Pat. No.______, which in turn claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/549,576 filed Oct. 20, 2011, both of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to methods and compositions for inhibiting theformation of hydrocarbon hydrates, and most particularly relates, in onenon-limiting embodiment, to methods and compositions for inhibiting theformation of hydrocarbon hydrates during the production of oil and gasusing polymeric kinetic hydrate inhibitors (KHIs).

BACKGROUND

A number of hydrocarbons, especially lower-boiling light hydrocarbons,in formation fluids or natural gas are known to form hydrates inconjunction with the water present in the system under a variety ofconditions—particularly at a combination of low temperature and highpressure (pressure and temperature are system-specific for the formationof gas hydrates). The hydrates usually exist in solid forms that areessentially insoluble in the fluid itself. As a result, any solids in aformation or natural gas fluid are at least a nuisance for production,handling and transport of these fluids. It is not uncommon for hydratesolids (or crystals) to cause plugging and/or blockage of pipelines ortransfer lines or other conduits, valves and/or safety devices and/orother equipment, resulting in shutdown, loss of production and risk ofexplosion or unintended release of hydrocarbons into the environmenteither on-land or off-shore. Accordingly, hydrocarbon hydrates have beenof substantial interest as well as concern to many industries,particularly the petroleum and natural gas industries.

Hydrocarbon hydrates are clathrates, and are also referred to asinclusion compounds. Clathrates are cage structures formed between ahost molecule and a guest molecule. A hydrocarbon hydrate generally iscomposed of crystals formed by water host molecules surrounding thehydrocarbon guest molecules. The smaller or lower-boiling hydrocarbonmolecules, particularly C₁ (methane) to C₄ hydrocarbons and theirmixtures, are more problematic because it is believed that their hydrateor clathrate crystals are easier to form. For instance, it is possiblefor ethane to form hydrates at as high as 4° C. at a pressure of about 1MPa. If the pressure is about 3 MPa, ethane hydrates can form at as higha temperature as 14° C. Even certain non-hydrocarbons such as carbondioxide, nitrogen and hydrogen sulfide are known to form hydrates underthe proper conditions.

There are two broad techniques used to overcome or control thehydrocarbon hydrate problems, namely the use of thermodynamic inhibitorsand Low Dosage Hydrate Inhibitors (LDHIs). LDHIs are referred to as suchdue to the low volume required to treat production streams when comparedto thermodynamic inhibitors. For the thermodynamic approach, there are anumber of reported or attempted methods, including water removal,increasing temperature, decreasing pressure, addition of “antifreeze” tothe fluid and/or a combination of these. The LDHI approach is furthersplit into two areas, Anti-Agglomerants (AAs) and kinetic hydrateinhibitors (KHIs). AAs prevent smaller hydrocarbon hydrate crystals fromagglomerating into larger ones and allow a mass of hydrates, sometimesreferred to as a hydrate slurry, to be transported along the conduit.KHIs however inhibit, retard and/or prevent initial hydrocarbon hydratecrystal nucleation; and/or crystal growth. Thermodynamic and kinetichydrate control methods may be used in conjunction.

Kinetic efforts to control hydrates have included the use of differentmaterials as inhibitors. For instance, onium compounds with at leastfour carbon substituents are used to inhibit the plugging of conduits bygas hydrates. Additives such as polymers with lactam rings have alsobeen employed to control clathrate hydrates in fluid systems. LDHIs arerelatively expensive materials, and it is always advantageous todetermine ways of lowering the usage levels of these hydrate inhibitorswhile maintaining effective hydrate inhibition.

Thus, it is desirable if new gas hydrate inhibitors were discoveredwhich would yield comparable or improved results over known gas hydrateinhibitors, and it is also desirable to find new, unexpectedapplications for gas hydrate inhibitors.

SUMMARY

There is provided, in one form, a method for inhibiting the formation ofhydrates that involves contacting a fluid that includes water andhydrate-forming guest molecules that form hydrates at hydrate formingconditions, with an amount of a kinetic hydrate inhibitor (KHI). The KHIincludes a copolymer or terpolymer made using monomers such asacryloylmorpholine, vinylimidazole, and/or vinylcaprolactam. The amountof KHI is that effective to inhibit hydrate formation at the hydrateforming conditions.

In another non-limiting embodiment herein, there is provided ahydrate-inhibited fluid that includes, water, hydrate-forming guestmolecules, and at least one KHI in an amount effective to inhibitformation of hydrates at hydrate forming conditions. Again, the KHIincludes a copolymer or terpolymer made using monomers such asacryloylmorpholine, vinylimidazole, and/or vinylcaprolactam.

In an alternate, non-restrictive version there is provided a copolymerformed by free radical polymerization from monomers includingacryloylmorpholine, vinylimidazole, and/or vinylcaprolactam.

Further in a different, non-limiting embodiment there is provided ahydrocarbon well having an annular space including fluid in the annularspace where the fluid is inhibited against hydrate formation in thepresence of water at hydrate forming conditions. The fluid compriseswater, hydrate-forming guest molecules, and at least one KHI in anamount effective to inhibit formation of hydrates at hydrate formingconditions. The KHI again includes a copolymer made from monomersincluding acryloylmorpholine, vinylimidazole, and/or vinylcaprolactam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a jar containing an intermediate copolymer ofacryloylmorpholine and vinylimidazole as synthesized; and

FIG. 2 is a plot of pressure as a function of time for a 3 vol % dosageof KHI B copolymer for 3 of 3 passes at 7° C. subcooling demonstratingconsistent hydrate inhibition until at least about 50 hours.

DETAILED DESCRIPTION

Methods and compositions have been discovered for inhibiting, retarding,mitigating, reducing, controlling and/or delaying formation ofhydrocarbon hydrates or agglomerates of hydrates in fluids used inhydrocarbon recovery operations. The method may be applied to prevent orreduce or mitigate plugging of annular spaces, pipes, transfer lines,valves, and other places or equipment downhole where hydrocarbon hydratesolids may form under conditions conducive to their formation oragglomeration.

The term “inhibiting” is used herein in a broad and general sense tomean any improvement in preventing, controlling, delaying, reducing ormitigating the formation, growth and/or agglomeration of hydrocarbonhydrates, particularly light hydrocarbon gas hydrates in any manner,including, but not limited to kinetically, thermodynamically, bydissolution, by breaking up, by anti-agglomeration other mechanisms, orany combination thereof. Although the term “inhibiting” is not intendedto be restricted to the complete cessation of gas hydrate formation, itmay include the possibility that formation of any gas hydrate isentirely prevented.

The terms “formation” or “forming” relating to hydrates are used hereinin a broad and general manner to include, but are not limited to, anyformation of hydrate solids from water and hydrocarbon(s) or hydrocarbonand non-hydrocarbon gas(es) known to form hydrates, growth of hydratesolids, agglomeration of hydrates, accumulation of hydrates on surfaces,any deterioration of hydrate solids plugging or other problems in asystem and combinations thereof.

The term “low dosage” used with respect to low dosage hydrate inhibitors(LDHIs) as defined herein refers to volumes of less than 15 volume %(vol %) of the water (water cut or water content) in the fluids beingtreated; alternatively less than 5 vol %. In some non-limitingembodiments, the vol % for thermodynamic hydrate inhibitors may beconsiderably higher, which depends on both the system subcooling andhold or residence time.

The present method is useful for inhibiting hydrate formation for manyhydrocarbons particularly including hydrocarbon and non-hydrocarbonmixtures. The method is particularly useful for lighter or low-boiling,C₁-C₅, hydrocarbon gases, non-hydrocarbon gases or gas mixtures atambient conditions. Examples of such gases include, but are notnecessarily limited to, methane, ethane, ethylene, acetylene, propane,propylene, methylacetylene, n-butane, isobutane, 1-butene,trans-2-butene, cis-2-butene, isobutene, butene mixtures, isopentane,pentenes, natural gas, carbon dioxide, hydrogen sulfide, nitrogen,oxygen, argon, krypton, xenon, and mixtures thereof. These molecules arealso termed hydrate-forming guest molecules herein. Other examplesinclude various natural gas mixtures that are present in many gas and/oroil formations and natural gas liquids (NGL). The hydrates of all ofthese low-boiling hydrocarbons are also referred to as gas hydrates. Thehydrocarbons may also comprise other compounds including, but notlimited to CO, CO₂, COS, hydrogen, hydrogen sulfide (H₂S), and othercompounds commonly found in gas/oil formations or processing plants,either naturally occurring or used in recovering/processing hydrocarbonsfrom the formation or both, and mixtures thereof.

The fluids treated may include, but are not necessarily limited to,drilling fluids, drill-in fluids, completion fluids, production fluids.In one non-limiting embodiment the fluids may be brines (e.g. chlorides,bromides, formates and the like). Suitable salts for forming the brinesinclude, but are not necessarily limited to, sodium chloride, calciumchloride, zinc chloride, potassium chloride, potassium bromide, sodiumbromide, calcium bromide, zinc bromide, sodium formate, potassiumformate, ammonium formate, cesium formate, and mixtures thereof. Thefluids may be placed in the annular space or other spaces downhole tofacilitate the production of hydrocarbons from the well. The method ofinhibiting hydrates is expected to be applicable where a fluid ispresent in a wellbore, a pipeline, an umbilical, a pipe, a transferline, a valve, a slug catcher and combinations thereof.

Suitable gas hydrate inhibitors for use in the methods and fluidcompositions herein may include, but are not necessarily limited to,copolymers and/or terpolymers of at least two different monomers, inparticular two or more of the group including acryloylmorpholine,vinylimidazole, vinylcaprolactam and/or n-vinyl pyrrolidone. Inparticular, it has been discovered that the copolymer ofacryloylmorpholine and vinylimidazole, as well as the terpolymer ofacryloylmorpholine, vinylimidazole and vinylcaprolactam, andcombinations thereof, are particularly useful.

The monomers are unsaturated and may be polymerized by free radicalpolymerization using any suitable free radical polymerizationinitiators. Such initiators include, but are not necessarily limited to,VAZO® 56 WSW initiator available from DuPont, VAZO® 68 WSP and otherVAZO® initiators, ammonium persulfate, di-tert butyl peroxide other azocompounds and peroxides. The polymerization proceeds easily, at atemperature between about 55 and about 75° C. at ambient pressure.Suitable chain transfer agents, modifiers or regulators include, but arenot necessarily limited to, 2-propanol (isopropanol; IPA),1-octanethiol, and the like. In the case of the copolymer ofacryloylmorpholine and vinylimidazole, the molar ratio ofacryloylmorpholine to vinylimidazole ranges from about 1:99 to about99:1; alternatively in a ratio of about 1:1. In the case of theterpolymer of acryloylmorpholine, vinylimidazole and vinylcaprolactam,the molar ratio of acryloylmorpholine to vinylimidazole tovinylcaprolactam ranges from about 1:1:98 to about 1:98:1 to about98:1:1. Alternatively, the molar ratio of the monomers in the terpolymermay range from those in the previous sentence to 33.3:33.3:33.3, inanother non-limiting embodiment to 40:20:40 and in a different,non-restrictive version to 45:10:45.

With more specificity and in one non-limiting embodiment the product maybe synthesized by a free radical polymerization mechanism. Methanol maybe used as the reaction solvent (although other similar solvents areexpected to be useful) and VAZO 56 WSW supplied by Du Pont may be usedas the free radical initiator. A 1:1 molar mixture of acryloylmorpholineand vinylimidazole may be charged to a reaction pot containing methanoland deoxygenated for 15 minutes by sparging with nitrogen. The freeradical initiator may be dissolved in methanol and also deoxygenated.The reaction pot may be heated to 65° C. and the initiator added to themonomer mixture over ten minutes maintaining the system under nitrogen.On completion of the addition the reaction may be left to stir at 65-67°C. for an hour after which time a viscosity increase may be observed. Afurther viscosity increase may be observed as the mixture is allowed tocool. The appearance of the mixture may be a pale yellow clear liquid,such as shown in FIG. 1. The weight percent of the active component inthe final product is approximately 25%. As will be discussed, hydrateinhibition tests on such a copolymer product were carried out usingstainless steel T-piece rocking cells without a viewing window andpressures monitored by the use of electronic pressure transducers. Acondensate (from the Ten Arlo field):water mix (75:25) was used as thesystem fluid. All tests were done at 7° C. subcooling varying the doserate of the product between 1-3 vol %. A Qatar Gas 3/4 synthetic gasmixture was used with a 48 hour rocking test period. The product gave3/3 passes at a 3 vol % dosage and 2/3 passes at a 1 vol % dosage.Improved performances in secondary property and compatibility testsdistinguish this product from the results obtained from known,commercial products. The new polymer is compatible in high salinitybrines at room temperature and at temperatures as high as 75° C.Alternative, existing products showed poor performances in these tests.

The contacting of the gas hydrate inhibitors herein with the mixture ofhydrocarbon, water and hydrate-forming guest molecules may be achievedby a number of ways or techniques, including, but not necessarilylimited to, mixing, blending with mechanical mixing equipment ordevices, static mixers, magnetic mixing or other suitable methods, otherequipment and means known to one skilled in the art and combinationsthereof to provide adequate contact and/or dispersion of the compositionin the mixture. The contacting can be made in-line or offline or both.The various components of the composition may be mixed prior to orduring contact, or both. If needed or desired, the composition or someof its components may be optionally removed or separated mechanically,chemically, or by other methods known to one skilled in the art, or by acombination of these methods after the hydrate formation conditions areno longer present.

Because the present compositions and methods are particularly suitablefor lower boiling hydrocarbons or hydrocarbon and/or non-hydrocarbongases at ambient conditions with no more than five carbon atoms, thepressure of the hydrate-forming condition is usually at or greater thanatmospheric pressure (i.e. greater than or equal to about 101 kPa),alternatively greater than about 1 MPa, and in another non-limitingembodiment greater than about 5 MPa. The pressure in certain formationsor processing plants or units could be much higher, say greater thanabout 20 MPa. There is no specific high pressure limit. The presentmethod can be used at any pressure that allows formation of hydrocarbongas hydrates.

The temperature of the condition for contacting is usually below, thesame as, or not much higher than, the ambient or room temperature. Lowertemperatures tend to favor hydrate formation, thus requiring thetreatment with the compositions described herein. At much highertemperatures, however, hydrocarbon hydrates may not form, thus obviatingthe need of carrying out any treatments.

It will be appreciated that it may be difficult to predict in advancethe proportions of gas hydrate inhibitors herein effective in inhibitinghydrocarbon hydrate formations in fluids any given situation. There area number of complex, interrelated factors that must be taken intoaccount in determining the effective dosage or proportion, including,but not necessarily limited to, the proportion of water in the fluid,the nature of the hydrocarbon, the nature of the hydrate-forming guestmolecules, the temperature and pressure conditions that the mixture ofhydrocarbon and water are subject to, the particular hydrocarbon hydrateinhibitor employed, etc. Experimentation with a particular set ofconditions or in a specific system may be a suitable way to determinethe optimum dosage range. Care should be taken to avoid the formation ofproblematic quantities of irreversible, harmful hydrate masses.Nevertheless, in the interest of attempting to provide some generalguidance of effective proportions, relative to the water phase, theamount of the KHI is from about 1 vol % independently to about 15 vol %,alternatively 8 volume % or less, and in another non-limiting embodimentranges from about 1 independently to about 5 vol %, and in onenon-limiting embodiment is less than 2 vol %. In one non-limitingembodiment the lower limit is independently about 0.01 volume %, andalternatively is about 0.1 vol % and possibly is about 0.5 vol %. Theterm “independently” as used herein with respect to a range means thatany lower threshold may be combined with any upper threshold to give asuitable alternate range.

In addition to the gas hydrate inhibitor herein, the hydrocarbon,inhibitor composition and the fluid may further comprise otheradditional components, including, but not limited to, differentcontrolling or inhibiting chemistries such as corrosion inhibitors, waxinhibitors, scale inhibitors, asphaltene inhibitors and other gashydrate inhibitors and/or solvents. Suitable solvents for the gashydrate inhibitors herein may include, but are not limited to water; atleast one oxygenated compound selected from C₁-C₆ alcohols, C₂-C₆glycols, C₁-C₆ mono-aliphatic, alternatively mono-alkyl, ethers of C₂-C₆glycol, glycerin, C₁-C₆ mono-aliphatic, particularly mono-alkyl, ethersof glycerin, C₁-C₆ di-aliphatic, particularly dialkyl, ethers ofglycerin, glycerin esters of C₁-C₆ carboxylate; tetrahydrofuran;N-methylpyrrolidone; sulfolane; C₃-C₁₀ ketones, and mixtures thereof.Examples of acceptable solvents in one non-limiting embodiment includewater and liquid oxygenated materials such as methanol, ethanol,propanol, glycols like ethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, glycerin, esters and ethers of glycerin,CELLOSOLVE® (2-ethoxyethanol), CELLOSOLVE derivatives, 2-propoxyethanol,2-isopropoxyethanol, 2-butoxyethanol, 2-isobutoxyethanol,2-methoxyethanol, ethoxylated propylene glycols, ketones such ascyclohexanone and diisobutylketone, and mixtures thereof. The solvent ispresent in the total hydrocarbon hydrate inhibiting composition in therange of from 0 wt % independently to about 85 wt %, alternatively fromabout 0 wt % independently to about 65 wt %, of the total composition,based on volume. CELLOSOLVE is a registered trademark of Union CarbideCorporation.

The polymers described herein also may be used in combination with othermethods or processes, which have been known to one skilled in the art asdiscussed in the Background to help inhibit formation of hydrates, aswell as other known hydrate inhibitors including, but not necessarilylimited to, onium compounds and dendrimeric compounds and in particularhyperbranched polyester amides.

The invention will now be described with reference to particularExamples which are not intended to limit the invention but rather simplyto illuminate it further.

EXAMPLES

The synthetic gas mixture used in testing had the composition as shownin Table I.

TABLE I Synthetic Gas Mixture Proportion Component 1.0 n-Butane 0.8 vol% Isobutene 1.8 vol % Carbon Dioxide 3.6 vol % Propane 5.2 vol % Ethane87.6 vol %  Methane

Example 1 Copolymer of Acryloylmorpholine and VinylimidazoleIntroduction

KHI A is a copolymer made up from two monomers: 4-acryloylmorpholine and1-vinylimidazole. The polymer has shown very encouraging performances inhydrate inhibition tests and has also passed a series of compatibilityand secondary property tests.

Preparation

KHI B was synthesized by a free radical polymerization mechanism. Theprocedure is quick and involves very few steps. Table II lists thereagents in the reaction and quantities used. It is also worth notingthat a large quantity of 2-propanol (IPA) used dramatically decreasesthe sample viscosity.

TABLE II Reagents for KHI B Quantity Reagent Supplier Purity Mol. Wt. mlg Moles Ratio Density B. pt. 4-Acryloyl- Aldrich 97% 141.17 10.8 12.10.085 50 1.122 158° C. morpholine (50 mmHg) Vinylimidazole Aldrich >99%94.12 7.7 8.0 0.0855 50 1.039 192-194° C. Methanol Fisher Tech. 32.04 6047.4 1.479 — 0.791 65° C. (pot) Methanol Fisher Tech. 32.04 40 31.60.986 — 0.791 65° C. (VAZO 56) VAZO 56 DuPont — 271.34 0.645 2.38 mmol 1 0.38 — initiator water — Deionized 18.02 20 20 1.110 — 1 100° C.

Procedure

Acryloylmorpholine (12.1 g), vinylimidazole (8.0 g), and methanol (60 g)were charged to a 500 ml reaction pot and degassed with nitrogen for 10minutes. The VAZO 56 WSW initiator (0.645 g) was dissolved in methanol(31.6 g) in a pressure equalising funnel and also degassed for 10minutes. The solution of monomers was heated to a temperature between65-67° C. and the initiator solution was added to the heated monomersolution as a single addition. The reaction was left to stir at 65-67°C. under nitrogen for an hour. The heat was removed and the polymerallowed to cool with stirring.

Hydrate Test Results

Hydrate tests were carried out using T-piece rocking cells. All testwork was done at 7° C. subcooling using Ten Arlo condensate. The testconditions in Table III were used.

TABLE III Hydrate Test Conditions Condensate: Ten Arlo condensate (70%)Aqueous phase DI Water (30%) Gas synthetic mixture Fill pressure 112 bar(11.2 MPa) Sub-cooling 7° C. Motion rocking-static-rocking Duration 168hours

The polymer was run in duplicate to verify performance andreproducibility. The results given in FIG. 2 show the KHI B gaveinhibition at 7° C. subcooling at 1.5 vol % dosage for up to 150 hours.

In addition to performing well in hydrate inhibition tests, the productmust undergo a series of secondary property and compatibility tests inorder to be considered further as a commercial product. These include ahot injection test, a foaming tendency test and an emulsion tendencytest.

Example 2 Hot Injection Test

This test determines how stable the polymer is at injection pointtemperature (whatever the injection temperature is at the specified gasfield). A Duran bottle containing the water/condensate mixture washeated to 90° C. using a temperature controlled stirrer hotplate. Onceat 90° C., the KHI was injected at the appropriate dose based on thewater cut. The solution is left at 90° C. for 1 hour then allowed tocool back below 30° C. Observations were taken throughout the test.Results are reported in Table IV.

TABLE IV Hot Injection Test Results Any notable Appearance Appearanceappearance Polymer at 90° C. immediately Appearance changes on refer-before after after 1 hr cooling back Pass/ ence injection injection at90° C. to <30° C. Fail KHI B Clear, con- Fluids Slight No changes Passdensation remain the cloudiness in on cooling bubbles same, no thebottom around emulsion or water layer the flask precipitate due to thepolymer.

Example 3 Foaming Tendency Test

In a 1 liter graduated cylinder with an internal diameter of 60 mm, amixture of 100 ml Ten Arlo condensate and 100 ml DI water is dosed with1.5 vol % KHI (based on water cut) and purged for two minutes with a 2.8liter/min N₂ flow through a sintered P2 glass tube. Both the initialfoam height and the time taken for the foam to collapse were recorded.The test temperature was ambient. A foam height of more than 500 ml or atime greater than one minute for the collapse is unsatisfactory anddisqualifies the KHI. The passing results are shown in TABLE V.

TABLE V Foaming Tendency Test Results Dose Foam Volume Time for FoamProduct (vol %) (mls) Collapse (sec) KHI B 1.5 <500 19

Example 4 Emulsion Tendency Test

A 70:30 Condensate/DI water mixture dosed with 1.5 vol % hydrateinhibitor (based on water) was agitated using an ULTRA TURRAX® disperserat 5000 rpm for 3 minutes. The mixture was left to settle for 10 minuteswith observations being taken: after sample addition; immediately afteragitating and after allowing it to settle for 10 minutes. A slighthaziness of the water phase due to a reverse emulsion is an acceptablefinal fluid condition. A heavy emulsion or pad (a pad is anon-collapsible emulsion or foam left between the two phases) constitutea failure. A blank sample is used as a benchmark. Results are given inTable VI.

KHI B passed all three of the secondary property tests.

TABLE VI Emulsion Tendency Test Results Product Dose (vol %)Observations after 10 minutes KHI B 1.5 The emulsion separates (after 2minutes) to leave a clear condensate layer. The aqueous layer remainshazy

Example 5 Compatibility Tests in DI Water and Brine

The polymer has to be stable in water at room temperature, sea-bedtemperature and elevated temperatures (usually the well-head injectiontemperature, which can vary from field to field). As applicationconditions may vary, a temperature of 90° C. was used as to represent arelatively high injection temperature.

100 ml of deionised water was added to a sample bottle and dosed with1.5% of the polymer sample (or the percentage to be used in the hydrateinhibition test). On observing the appearance at room temperature, thebottle is heated to 90° C. for in a water bath, after 15 minutes finalobservations were taken. A 1.5 vol % dosage was used. Results arepresented in Table VII. “CBL” refers to Clear Bright Liquid—this meansthe sample has not suffered detrimental precipitation or component“fall-out” after heating and is stable to the process; no haziness isapparent.

TABLE VII DI Water Compatibility Test Results Appearance at Appearanceat Polymer room temperature 70° C. KHI A CBL CBL

Similar tests were repeated with a low salinity brine (10,000 TDS (totaldissolved solids)) and a high salinity brine (180,400 TDS). Again, a 1.5vol % dosage was used. The results are presented in Table VIII. It canbe seen that KHI B passed all the water/brine compatibility tests.

TABLE VIII Brine Compatibility Test Results Brine concentration PolymerAppearance at Appearance at (TDS) reference room temperature 70° C.10,000 KHI B CBL clear - no precipitate 180,400 KHI B CBL clear - noprecipitate

Example 6 KHI C—Terpolymer of Acryloylmorpholine, Vinylimidazole andVinylcaprolactam

The synthesis of the KHI (terpolymer) was performed in a two piece glassreactor with 5 ports available for ancillary equipment including:overhead mechanical agitator, reflux condenser, dropping funnel,thermocouple and stopper. The empty vessel was placed on a tared balanceand the reagents added by weight. The monomers: 4-acryloylmorpholine,(11.60%), N-vinylimidazole, (7.73%); 1-vinylcaprolactam (2.53%) methanol(52.76%) and 2-propanol (IPA)(16.92%) were added to the vessel anddegassed for a period of five minutes before heating to 65° C. Anaqueous solution of VAZO 56 WSW initiator (herein referred to as VAZO)was also degassed for five minutes or until the solid initiator wasdissolved. The initiator solution comprised 0.50 g VAZO in 4.98 g water.A head of positive nitrogen pressure was maintained throughout thereaction to reduce any air ingress potentially capable of killing freeradicals and preventing their propagation through the mixture.

When the monomer solution reached 65° C., the VAZO solution was added tothe monomer solution in a single addition. If the reaction was on ascale larger than about 1 kg (total mass) the VAZO solution may be addedin a stepwise fashion to control the exotherm produced. The reaction wasallowed to proceed with mechanical agitation for 90 minutes or until thereaction was deemed complete by non-volatile residue analysis. The clearyellow solution was allowed to cool with stirring until ambienttemperature was achieved.

The cooled mixture appeared slightly cloudy and was weighed to determineany weight loss due to solvent losses over the course of the reactionperiod. Any lost solvent was replaced with methanol (the component mostlikely to be lost) to maintain the original mass. Water (2-3 percent)was added to the cloudy mixture and stirred until the mixture becamecompletely clear.

Current KHIs are obtained from suppliers and prepared by blending withspecific solvents. Improved performances in secondary property andcompatibility tests distinguish this terpolymer product from current KHIproducts.

The new polymer was compatible in high salinity brines at roomtemperature and at temperatures as high as 75° C., as determined by thetests described in Example 5. Current products showed worse performancein these tests. The KHI was added to a hydrate rocking cell (eithersightless or with a viewing window) as a percentage of the water in theproducing gas system being modeled. Condensate may also be added tomimic the modeled system. Finally, a synthetic or real (natural) gasmixture was added to the cell under pressure until the desired pressurewas obtained to achieve the system's subcooling at the test temperature.The cell(s) were added to a water bath and the water temperature waslowered to achieve the desired subcooling (in combination with thepressure used) for the system to be effectively modeled. The pressuresof the cells were monitored and recorded electronically. The terpolymerperformed well in the hydrate test and passed.

The compositions and methods herein may be improved if the chemical orsolvent balance is altered in favor of one chemical or another, or ifadditional monomers are included in the product. Alternate chaintransfer agents or reaction solvents not tried above but within thescope of the methods and compositions herein may also have a positiveeffect on the outcome of the KHI's properties. The reaction time for theprocess could vary from as little as 1 minute to several hours and theaddition of the initiator could take place over a shorter period (i.e.as a single and instant addition) or a longer period. Differences inreaction temperatures could be observed and the degassing process may ormay not need to occur. The product could also be synthesized by otherstep or chain growth polymerization processes such as RAFT (reversibleaddition-fragmentation chain transfer), metathesis, anionic or cationicpolymerizations.

Further, the bias of the chemicals within the KHI may be altered toimprove or fine tune the desired properties of the polymers. Theseproperties may be the primary KHI performance to inhibit the onset ofgas hydrates or secondary properties such as emulsion or foamingtendencies, improved stability in hot injection tests, thermalstability, environmental impact, compatibility with other commonly usedchemicals such as corrosion or other inhibitors. In addition, thecomposition may be altered to increase cost effectiveness or to finetune to a particular application.

Many other modifications may be made in the compositions and methods ofthis invention without departing from the spirit and scope thereof thatare defined only in the appended claims. For example, the exactcopolymers and terpolymers may be different from those explicitlymentioned herein. Various combinations of gas hydrate inhibitors aloneor together other than those described here are also expected to beuseful. Further, LDHIs used alone or together with mixtures of water,hydrocarbons and hydrate-forming guest molecules different from thoseexemplified herein would be expected to be successful within the contextof this invention.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For instance, a method forinhibiting formation of hydrates may also consist essentially of orconsist of contacting a fluid including water and hydrate-forming guestmolecules that form hydrates at hydrate forming conditions, with anamount of a kinetic hydrate inhibitor (KHI) effective for inhibitinghydrate formation at the hydrate-forming conditions consisting essentialof or consisting of a copolymer having monomers selected from the groupconsisting of acryloylmorpholine, vinylimidazole, vinylcaprolactam andcombinations thereof. Also, a hydrate-inhibited fluid may also consistessentially of or consist of water, hydrate-forming guest molecules, andat least one kinetic hydrate inhibitor (KHI) in an amount effective toinhibit formation of hydrates at hydrate forming conditions, where theKHI consists essentially of or consists of a copolymer having monomersselected from the group consisting of acryloylmorpholine,vinylimidazole, vinylcaprolactam and combinations thereof. Additionally,a copolymer may consist essentially of or consist of monomers selectedfrom the group consisting of acryloylmorpholine, vinylimidazole,vinylcaprolactam and combinations thereof. Further, a hydrocarbon wellmay consist essentially of or consist of an annular space and a fluid inthe annular space, where the fluid is inhibited against hydrateformation in the presence of water at hydrate forming conditions, andthe fluid consists essentially of or consists of water, hydrate-formingguest molecules and at least one kinetic hydrate inhibitor (KHI) in anamount effective to inhibit formation of hydrates at hydrate formingconditions, where the KHI consists essentially of or consists of acopolymer having monomers selected from the group consisting ofacryloylmorpholine, vinylimidazole, vinylcaprolactam and combinationsthereof

The words “comprising” and “comprises” as used throughout the claims isto interpreted “including but not limited to”.

What is claimed is:
 1. A hydrate-inhibited fluid comprising: water;hydrate-forming guest molecules; and at least one kinetic hydrateinhibitor (KHI) in an amount effective to inhibit formation of hydratesat hydrate forming conditions, where the KHI comprises a copolymercomprising monomers selected from the separate groups consisting of:acryloylmorpholine, vinylimidazole, vinylcaprolactam, and combinationsthereof; and acryloylmorpholine, vinylimidazole, n-vinyl pyrrolidone andcombinations thereof.
 2. The hydrate-inhibited fluid of claim 1 wherethe copolymer is selected from the group consisting of a copolymer ofacryloylmorpholine and vinylimidazole.
 3. The hydrate-inhibited fluid ofclaim 2 where in the copolymer of acryloylmorpholine and vinylimidazole,the molar ratio of acryloylmorpholine to vinylimidazole ranges fromabout 1:99 to about 99:1.
 4. The hydrate-inhibited fluid of claim 1where the effective amount of the KHI in the fluid ranges from about 1to about 15 vol % based on the water in the fluid.
 5. Ahydrate-inhibited fluid comprising: water; hydrate-forming guestmolecules; and from about 1 to about 15 vol % based on the water in thefluid of a kinetic hydrate inhibitor (KHI) in an amount effective toinhibit formation of hydrates at hydrate forming conditions, where theKHI comprises a copolymer of acryloylmorpholine and vinylimidazole,where the molar ratio of acryloylmorpholine to vinylimidazole rangesfrom about 1:99 to about 99:1.
 6. A copolymer comprising monomersselected from the separate groups consisting of: acryloylmorpholine,vinylimidazole, vinylcaprolactam, and combinations thereof; andacryloylmorpholine, vinylimidazole, n-vinyl pyrrolidone and combinationsthereof.
 7. The copolymer of claim 6 where the copolymer is a copolymerof acryloylmorpholine and vinylimidazole.
 8. The copolymer of claim 7where in the molar ratio of acryloylmorpholine to vinylimidazole rangesfrom about 1:99 to about 99:1.